Electromagnetic friction device



Jan. 26, 1937. A. B; C DM AN 2,068,654

7 ELECTROMAGNETIC FRICTION DEVICE Filed Dec. 10, 1934 2 Sheets-Sheet lJan. 26, 1937.

A. B. CADMAN ELECTROMAGNETIC FRICTION DEVICE Fil ed Dec. 10, 1934 2Sheets-Sheet 2 nan;

MTOQ/ Patented Jan. 26, 1937 UNITED STATES PATENT o FicE 2,068,654ELECTROMAGNETIC FRICTION DEVICE Addi B. cam, Beloit, Wis.

Application December 10, 1934, Serial No. 756,760 8 Claims. (01.188-140) This invention relates to electromagnetic friction devices forbrakes and clutches, and more particularly to those in which africtional force is derived by electromagnetic attraction between asubstantially flat annular armature ring and the concentric pole facesof a second ring carrying an electromagnetic winding.

One object of the invention is to provide, in an electromagneticfriction device of the above character, a novel construction andmounting of the magnetic armature by which the detrimental effect ofresidual magnetism is eliminated effectually. I

Another object is to provide an armature construction which is notsubject to objectionable distortion under the heat developed duringfrictional engagement ofthe magnetic parts.

A further object is to provide-a novel armature mounting by which anaccurate relation between the energizing current and the attractiveforce of the magnetic rings may be obtained in initial manufacturewithout accurate machining of the coacting faces of the magnetic rings,which relation is maintained effectively through long periods of actualservice use of the friction device.

Other objects and advantages "of the invention will become apparent fromthe following detailed description taken in' connection with theaccompanying drawings, in which Figure 1 is a diametrical sectional viewof an electric brake equipped with frictiondevice embodying the featuresof the present invention.

Fig. 2 is a face view of the armature unit con- 'structed in accordancewith the present invention.

Fig. 3 is a fragmentary sectional view taken substantially along theline 3--3 of Fig. 1.

' Fig. 4 is a sectional view taken along the line 44 of Fig. 2.

Fig. 5 isan enlarged sectional view taken along the line 5-5 of Fig. 2.

While the invention is susceptible of various modifications andalternative constructions, I have shown in the' drawings and will hereindescribe in detail the preferred embodiment, but it is to be understoodthat I do not thereby intend ,to limit the invention to the specificform disclosed, but intend to cover all modifications and alternativeconstructions falling within the spirit and scope of the invention asexpressed in the appended claims.

In the drawings, the invention is embodied in an electric brake for avehicle wheel 6- including a rotatable drum 1 having the usual flange 8bolted or otherwise secured to the wheel hub 9. The inwardly opening endof the drumis closed by an annular plate Ill suitably secured to anon-rotatable support (not shown). The non-rotatable friction surface ofthe brake is of the band type comprising a metal strip ll encirclinginwardly projecting flange i 2 on the anchor plate and carrying segmentsI3 of friction material. Fittings M are secured to the opposite ends ofthe strip ii and drawn by a spring 15 into abutting engagement with theopposite end surfaces of a stop it rigid with the anchor plate.

The electromagnetic operator in which the present invention isembodiedis utilized to spread the ends of the band'apart and thereby set thebrake. It comprises two rings I! and 18 of magnetic material arrangedconcentric with the drum and adapted for axial gripping engagement.Preferably, the ring IT, which constitutes the magnetic armature, issubstantially flat and of solid metal construction, being floatinglysupported from the drum so .as to rotate therewith and at the same timeadapted for some degree of axial movement. To this end the back of thering is secured at annularly spaced points to the ends of flexible metalstrips [9 which extend in a substantially tangential direction and arerigid at their other ends with a ring 20 in turn riveted to the drumflange 8. The strips l9 are tensioned to urge the armature ring I1 awayfrom the drum flange and thereby maintain the face of the ring inconstant light mechanical contact with the face of the'magnet I8. Thestrips act in tension to prevent relative rotation between the rings I1and 20 in one direction. Relative rotation in the other direction isprevented by engagement between lugs 2| rigid with the armature andflanges 22 rigid with the ring 20.

The ring l8 constitutes a magnetic core and is U-shaped in cross sectionwith a winding 23' disposed between and enclosed by its two concentricpoles 24 and adapted to be energized from g a storage battery or-othersource of electrical power. Plates 25 of non-magnetic material aremounted between the poles and provide a wear resisting surfacesubstantially flush with the end faces of the poles and adapted tosustain the axial pressure between the two magnetic rings. The magnetring is supported for oscillation about the drum axis by a circularflange portion 26 of the anchor plate. I 4

Projecting rigidly from the outer magnet pole are two actuatinglugs 21having oppositely facing surfaces positioned to abut against lugs 28attraction of the magnetic parts upon the sub-' band. Upon movement ofthe magnet in either direction away from normal brake-released position(Fig. 8), one or the other of the lugs 21 will move its end of the-brakeaway from the stop ll, thereby expanding the band and pressing itsentire friction surface against the drum.

Such actuation of the band takes place whenever the-winding 23 isenergized with the wheel in motion. This produces a magnetic flux ofhigh intensity in the closed magnetic circuit which encircles thewinding through the opposite sections of the magnet core and armature.The re-- sulting magnetic attraction causes gripping engagement betweenthe friction surfaces of the two rings proportional to the strength ofthe energizing current, whereupon the magnet ring will be drivenfrictionally by the armature ring thereby moving with the wheel a shortangular distance. In this circumferential movement, one end of the bandis moved away from the stop l6 expanding the band and thereby pressingthe segments l3 against the drum surface. After the normal clearance.has been taken up, angular.

movement of the magnet ceases causing slippage between the ring surfacesin the continued rotation of the wheel. When the current flow isinterrupted; the spring i5, acting through the medium of the fitting l4and the lug 21 serves to restore the magnet as well as the actuated endof the band to normal brake-released position.

Inasmuch as the friction faces of the rings l1 and II are constantlyurged into light mechanical contact by the springs i9 while the winding23 is deenergiaed, it is unnecessary for the magnetic flux produced bythe initial energization of'the winding to overcome an air gap of anysubstantial width between the rings. As a result, the attractive forceand, therefore,- the degree of braking action is directly proportionalto the strength of the energizing current.

A magnet of the character above described is capable of producing anextremely powerful attractive force when energized by a relatively lowcurrent owing to the extremely low reluctance of the magnetic fluxcircuit which encircles each circumferential section of the winding 23.For.

this reason, the residual magnetic fleld which inherenth! exists in themagnet core following such current interruption, tends to maintain .thefriction elements under some degree of gripping pressure. Such apersistent drag, if allowed to exist, would be particularly detrimentalin a brake of the above character not only because of the lightretarding action which-it exerts on the wheel but because it subjectsthe magnetic elements to constant frictional wear and unneces saryheating.

The present invention contemplates elimination of the detrimentaleffects of residual magnetism by so constructing the armature II thatone side edge thereof will, when the magnet is deenergized, be movedmechanically away from the coacting pole of the magnet therebyintroducing inthe magnetic circuit around the entire periphery of themagnet an air gap of dimensions sufficient to dissipate the residualmagnetism instantaneously but not so wide as to prevent proper sequentenerglzation of the magnet. To this end, the armature ring is formedwith a friction surface of slightly conical contour, the metal of thearmature possessing sumcient resiliency to cause this conical curvatureto be assumed and one side of the armature ring to spring away from thecoacting magnetic pole when the magnet is deenergized.

To permit of such action, the armature ring is formed in a plurality ofstructurally separate sections (see Fig. 2) which are mechanicallyconnected by metallic strips 30 forming in effect a. continuous ringstructure but permitting of suflicient relative movement between thesegments to enable them to be drawn down into firm contact with the faceof the magnet when the latter is energized. As shown in Figs. 2 and 4,the strips 30 are located at the outermost edge of the armaturesegments, and their opposite ends are secured as by welding-to the backof the adjacent segments. The spring strips 15, by which the armaturering is supported. are in turn secured as by welding to the strips 30.

The coned surface of the armature ring may be formed by distorting theindividual segments as in a pressing operation. The degree of coning isonly a few thousandths of an inch across the face of the armature, being.008 of an inch in the present instance. With the armature thusconstructed, it will be seen from Fig. 5 that the inner edge of thesegments I! will be spaced a small distance from the inner magnet polewhenever the magnet is deenergized. When current is ap plied to thewinding 23, the resulting attractive force produced will distort thesegments ll sufficiently to draw their inner edges into firm mechanicalcontact with the magnet face and against the inner pole face. With thesegments thus stressed, it will be apparent that they will tend toassume their coned condition upon deenerglzation of the magnet so thatas soon as the current to the winding 23 is interrupted, the inner edgesof the segments will spring away from the inner magnet pole and therebyintroduce around the entire magnetic circuit a non-magnetic gap ofsufficient width to dissipate the residual magnetism. This action willcontinue throughout the service life of the friction device.

The segmental armature construction above described is also advantageousin that it possesses sufficient flexibility to allow the armature toadapt itself to the magnet surface in spite of distortion thereof whichmay occur in joining the parts together or under the heat incident tothe service use of the device. Thus, it has been found to be unnecessaryto grind the face of the armature ring I1 after the ring and itssupporting elements have been assembled. In addition, magnet andarmature units may be constructed which will therefore produce the sameconsistent action in the frictiondevlce when energized by a givencurrent.

I claim as my'invention:

1. An electromagnetic friction device combining a magnet ring having twoconcentric pole faces disposed in a plane perpendicular to the ringaxis, an annular-winding carried by said ring and disposed between saidpoles, and a second ring of magnetic material adapted to be brought intofrictional gripping engagement with said first ring and overlying saidpoles so as to form a magnetic flux circuit encircling all sections ofsaid winding, said second ring comprising relatively movable sectionsadapted to lie flat against the face of the magnet when the latter isenergized but stressed to spring away from one of said pole faces anddefine a conical surface when the magnet is deencrgired.

2. An electromagnetic friction device combinnc a magnet ring having twoconcentric polefaces disposed in a plane perpendicular to the 1 aoeaouring axis, a winding carried by said ring and disposed between saidpoles, and a second ring of magnetic material adapted to be brought intofrictional gripping engagement with said first ring and overlying saidpoles so as to form a magnetic flux circuit encircling all sections ofsaid winding, said second ring being composed of relatively movablesections and the surfaces thereof overlapping said pole faces having aslightly conical contour.

3. For use in an electromagnetic friction device, an armature ringcomprising a plurality of fiat metal segments arranged in end to endrelation and defining an annular friction face of slightly conicalcontour, and means on'the side of said segments opposite said faceconnecting the sections together to form a unitary ring while permittingrelative flexing of the sections to bring all points of said frictionsurface into a common plane.

4. An electromagnetic friction device comprising, in combination, amagnet ring carrying a winding and having two concentric pole facesdisposed in a plane perpendicular to the ring axis, and a coactingarmature ring composed of relatively movable segments defining afriction face overlapping said :ooie faces and having a conical contoursuch that the armature is disposed further from the inner than from theouter pole face when said winding is deenergized.

5. An electromagnetic friction device comprising, in combination, amagnet ring carrying a winding and having two concentric pole facesdisposed in a plane perpendicular to the ring axis, a coacting armaturering having a friction face overlapping said pole faces and tiltablerelative to the latter by mechanical action when the magnet ring isdeenergized whereby to introduce an air gap between the armature ringand one of said pole faces, and means operating while the magnet isdeenergized to maintain mechanical contact between the rings at pointsadjacent the other pole face.

6. An electromagnetic friction device comprising, in combination, amagnet ring carrying a winding and having two concentric pole facesdisposed in a plane perpendicular to the ring axis, a coasting armaturering having a friction face overlapping said pole faces and arranged tobe tilted mechanically relative to said magnet ring in a direction tointroduce an air gap between the armature and the inner one of said polefaces, and means acting while the magnet is deenergized to maintain thearmature ring substantially in contact with the outer pole face.

i 7. For use in an electromagnetic friction device, an armature ringcomprising a plurality of fiat metal segments arranged in end to endrelation and defining an annular friction face of slightlyconicalcontour, and metal strips connecting the adjacent ends of saidsegments and disposed adjacent one side edge of the segments.

8. An electromagnetic friction device comprising a magnet and anarmature therefor having Leooperating annular faces, said armaturecomprising a plurality of segmental sections and metal strips joiningthe adjacent ends of said sections to form a substantially rigid unitarystructure while permitting of some degree of relative flexibilitybetween the sections. l

ADDI B. CADMAN.

